Aromatic polyimide films show good high temperature resistance, good chemical properties, high electrical insulating property, and high mechanical strength, and therefore are widely employed in a variety of technical fields. For instance, an aromatic polyimide film is favorably employed in the form of a continuous aromatic polyimide film/copper foil laminate structure for manufacturing a flexible printed circuit board (FPC), a carrier tape for tape-automated-bonding (TAB), and a tape of lead-on-chip (LOC) structure.
The aromatic polyimide film/copper foil laminate can be produced by bonding a polyimide film to a copper foil using a conventional adhesive such as an epoxy resin. However, due to low heat-resistance of the conventional adhesive, the produced composite sheet cannot show satisfactory high heat-resistance.
For obviating the above-mentioned problem, a variety of bonding methods have been proposed. For instance, an aromatic polyimide film/copper foil laminate sheet is manufactured by producing a copper foil on an aromatic polyimide film by electro-plating. Otherwise, an aromatic polyamide solution (i.e., a solution of a precursor of an aromatic polyimide resin) is coated on a copper foil, dried, and heated for producing an aromatic polyimide film on the copper foil.
An aromatic polyimide film/copper foil composite sheet also can be produced using a thermoplastic polyimide resin.
U.S. Pat. No. 4,543,295 describes that a metal film/aromatic polyimide film laminate in which the metal film is bonded to the polyimide film at a high bonding strength is prepared by combining, namely by heating under pressure, a metal film and a composite aromatic polyimide film composed of a highly heat resistant substrate film and a thermoplastic thin polyimide layer bonded to the substrate film at a high bonding strength.